[rescue] Serial console - break "filtering" connection - resistor method

[Brandon Applegate]

So the NUD4273… From:

https://www.usenix.org/events/lisa00/full_papers/drzyzgula/drzyzgula.ps

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It contains fifteen resistors, eight diodes, three transistors, one op amp and five capacitors – one of them a large 1000uF electrolytic.
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Finally found a picture:

https://web.archive.org/web/20010614020819/http://www.nudata.com/pdf/4273_Sellsheet.pdf

Man I’d love to be able to clone that.

Sent from my phone

> On Oct 16, 2023, at 6:50 PM, vom513 <vom513 at gmail.com> wrote:
> 
> Hello all,
> 
> So I have a couple of dumb terminals (the one I’m using to test now is a WYSE-160).  I’m using an IPX as the test machine.  So this has the DIN-8 to DB25 cable.
> 
> As we all know, by default, when dropping the console connection (i.e. turning the terminal off) - Suns will drop to PROM/debugger :(
> 
> Years ago there was supposedly a pricey cable/dongle (NuData 4273) that would “shield” the Sun from break signals.  Another hardware solution I’ve seen mention of is putting a resistor in the connection to disable break signals.  This is the rabbit hole I’m going down.
> 
> I’m trying to use this:
> 
> https://hea-www.cfa.harvard.edu/~fine/Tech/cs1.2/Sun-serial
> 
> According to that, we are pulling -5v off pin 25, running it through a 4.7k resistor, and connecting this to pin 3 on the Sun side ?  Am I reading that correctly ?
> 
> On my IPX - I seem to get nothing off pin 25 (testing with DMM, and tried the shield as well as pin 7 as ground).
> 
> I do however seem to get -5v off pin 1.  If I’m reading that Harvard URL right - I should be able to use pin 1 in place of 25 ?  I’m leery of this as I’d really rather not blow up the serial port and/or machine itself…
> 
> So any info anyone can give me on this would be greatly appreciated.  I’d really like to be able to power my dumb terminal off/on as well as use a serial switchbox without dropping the box(es) to PROM.
> 
> Thanks.
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